Telephone privacy



Aug. 27, 1946 w. A. MUNSON TELEPHONE'PRIXIIACY Filed Feb. 11, 1942 2Sheets-Sheet 2 FIG. 4

lNl ENTOR WAMUNSON A TTORNEY Patented Aug. 27, 1946 UNITED STTES r'rsnrFFICE TELEPHONE PRIVACY Application. February 11, 1942, Serial No.430,370

9 Claims.

The present invention relates to the use of rotary distributors forsubdividing message waves on a time basis for transmission or reception.More particularly the invention relates to the problem of coordinatingthe movements of a recording medium such as a magnetic tape and a rotarydistributor located at one point to the movements of similar apparatusat a distant point.

The invention will be disclosed, for illustration, as embodied in aspeech privacy system in which speech is recorded on a moving magnetictape and is subdivided on a time basis by a rotary distributor soarranged as to send out the fragments of speech in abnormal sequence tomake reception by unauthorized persons difficult. A similar magnetictape recorder and rotary distributor at the receiving point subdividethe received privacy speech and rearrange its parts into understandablespeech.

It has been proposed heretofore to use various types of start-stopdistributors for securing synchronism between the switching operationsperformed at separated stations in reproducing the recorded speechfragments and transmitting them in altered sequence. Where the brushesare stopped in their motion relative to the distributor segments once ineach revolution, they must be quickly accelerated again when started andthis sudden transition in both stopping and starting not only places astrain on the mechanism but can give rise to errors due to the variableaccelerate time under different conditions. This has been true in priorart systems where all machines, both those running in exact synchronismand those having an error, are subjected to this stopping and startingin each revolution.

The present invention involves a species of start-stop operation but thebrushes themselves are never actually stopped so long as they arerunning in exact synchronism. In a system involving a number ofmachines, only those operating with a speed error are subjected to thestopstart action of the brushes so that the machines running normallyare not penalized by the fact that other machines may need correcting.

It is common practice in printing telegraphy to use start-stopdistributors and to run th receiving distributor normally slightlyfaster than the transmitting distributor so that normally it is stoppedfor a longer time, in each revolution, than the transmittingdistributor. Errors in speed of the receiving distributor result inVarying the duration of stoppage of the receiving distributor, and byrunning the receiving distributor starting pulses.

normally too fast a greater margin is allowed in stoppage time tocompensate for speed variations. If the receiving distributor varies inspeed by becoming still faster the stoppage period is:prolonged. If thevariation is a slowing down, the stoppage time is reduced. It iscustomary in such systems to make the receiving distributor segmentsshorter than the transmitter segments so as to pick out the middle partof the transmitted pulse.

In a speech privacy system in which rotary distributors are used tosubdivide the message waves as referred to above, the synchronizingpresents a much more difficult problem since it is necessary to preserveas far as possible the entire'wave, which means that ideally eachtransition of the two distributors from one segment to the next shouldbe made at the same instant and with minimum transition time. Moreover,if the same apparatus is to be used alternatively to transmit andreceive for purposes of two-way conversation, the distributors must becapable of serving for either transmitting or receiving and cannot beofdifferent design. 1w

It is possible to secure some of the advantage of running the receivingdistributor slightly fast, by actually running it at the sameconstantspeed as the transmitting distributor but delaying slightly thesending out of the start impulse so that both distributors are normallystopped for an interval to allow a time margin in which to correct forerrors in speed of the receiving distributor. This enables alldistributors to be alike in construction, and when any distributor isconverted from receiving to transmitting it is arranged, automaticallyto send out thedelayed All receiving distributors are then synchronizedto the distributor that is at' the time transmitting. r r

The invention possesses certain of the. advantages obtained by use ofthe delayed startin pulse but avoids the attendant loss of a smallpercentage of the speech which has been experienced with certain typesof apparatus using the delayed impulse method and avoids the stopping ofthe brush itself except when itis out of normal phase position.

In accordance with the embodiment of the invention to be specificallydisclosed herein,=-the stop for the brushes is itself carried on arotating arm so arranged that if the brushes are running at normal speedthe stop is removed as'the brush carrier comes up against it, and nostoppage of the brushes occurs. If the brushes are-running in advance ofnormal they are stopped'momen- Figs. 4 and 5 are respectively views inplan" and elevation, partly in section, of rotary-distributor mechanismconstructed in accordance with the invention; and V v Fig. 6 shows adetail of the movable stopin relation to the brush carrier.

The over-all system as"diagrammed-inFigpl will first be described. Thissystem as shown is assumed to be the same as that disclosed inapplication for United States Letters Patent Serial #No. 401;908 :Iof i.G, :Buhrendorf filedlJuly ll, 1- 1941,:an'd only a cbrief descriptionof-ittwill be cgivenfifhere sufficient to show how the. improved-idistributor mechanism of the invention maybe inserted into the system.

IniFigil a motor I (Lthrough a shaft? 9 l,;drives hrush- 13: ofca rotarydistributor and also .drives easwheel:(ndthhown) having a magnetic tape"mounted on its rimzso asto move past the polepieces of a recordingmagnet l9 and a number .iWhen; stationliis usecLfor transmitting, mi-

v'cnoph-one'. I 'kisFspoken into and the1contacts in 'i the boxf 23,labelled talkreceive oircuittare put in'italkingposition so'that thespeech waves: are '.';sent: to recordingfmagnet I I 9.this'recorded'speech moves along past therepro- The tape bearing:ducer'rmagnets: in succession and is reproduced inxeachiof 'themninsuccessive: phase. The'code :".switches in box- 24, and the talkreceiveswitches f'ithereinpareiset:soas to connect certain specifiedOIlGS'IJOf these reproducerzmagnets 'to ,the five pairs of segments ofdistributor'ring .29 in acricordanceewith the particular code beingused. theibrusharmii (after being released) sweeps iovertthesetsegmentsithe brush :bridges :the; seg- ;:ments:- in.- succession to the ring Lt!)so that .the sspeechffra'gments are sent over leads and:throughcontactsr in box 23: tooutgoing. line or achannel 22 leading to:station 2.

"a'Ihe shaft II also drives through gearsle'and 1-5; with slight speedreduction, arotaryicontact :maker in; the startimpulse circuit '25 whichsends ea start impulseitozrelease magnet tie-once each -revblution andalso to outgoingline'22 through :leadsZlcandcontacts in box 23.to startthe :dis- .itributorrbrushes-of 'both stations .at theisame instant.

Inthel Buhrendorf disclosurethe brush .arm -I 3':isfrictioncdrivenbyshaft H that it may be stopped -while the shaftcontinues to rotate.

':The tNo.'i5 segment .on which the brush is shownrestingyina-Fig.lisshorter than the other. seg

mentsrandthe; relation is suchv that the normal .stOppa etime on'thisshort segment plusthe travel time across this segment both before andafter the stoppage is just equal to thenormal .;time; of traveltof E.the brush across each: of the :Qther segments.- xThis is coordinatedwith z the flQiBIQrYQiH t'hB sending of the start impulse (due 'to nthegearrreduction'ratio,of gear train it, l5) so.

--.that 'i'whenr-a ll machines are running: normally .-thes;. d;urationof the stoppage interval ;of :the

;-brushesz is. the same in all-machines. If a-receiv- 30' =iofreproducing'magnets'ia.as more'fully shown --:-in"theiBuhrendorfdisclosure.

4 ing machine is slightly slow, the stoppage interval is shortened; ifslightly fast, the stoppage interval is prolonged, in each case by theamount necessary to insure starting of all brushes at the same time.Whatever error exists within the capability of the mechanism to'correctit, is in this way wiped out at the conclusion of each rotation of thebrush and is prevented from accumulating. The receiving machine ormachines are governed from the sending machine by the sending out of thestart impulse.

When the apparatus in Fig. 1 is used to receive from distant station 2,contacts are thrown in boxes 23, 2 3,. and v26 at each station so thatstationl ends out the start impulse and the speech fragments inaccordance with the code previously agreed upon. The speech fragmentsreceived over line 22 pass through contacts in box 23 to recordingmagnet i9 and the start impulses are sent through contacts in box 26 tothe winding of release magnet 33; The reproducer ,magnets'22 pick 01fthe recorded speech segments from the moving tape and these are sentthrough 7 contacts of the code switches to the five pairs ofdistributorsegments 29 in such manner that they are'swept off by thebrush in normal speech order and sent to receiver is over leads-25 andcontacts in box 23 in receiving position; The brush arm I3 is stopped atthe end of each rotation by latch 32 and is released in time corre--spondence with the distant transmittingdistributor under control of thestart impulses.

In the construction accordingto the present invention all of thecommutator segments have equal length and there'is no stoppage of thebrushes on any commutator segment unless the brushes are running toofast andneedito'be stopped inorder to be brought into; proper startingphase. The'principle-of operation is -illustrated in the diagrams ofFigs. 2 and 3. is a corrector arm' la driven slightly faster than thebrush carrier A t-represented as a ring (actually it may be an arm)having a small'arc cut to present two limits as and'etto the relativemovement of arm '43 with respect to :ring Hi. In Fig. 2 the normalrelation is shown at the instant-of release of corrector-armes for thestart of a rotation, the limit #25 just reaching the arm tl3 as thelatter is released, so that the'movement of brush: ring as isuninterrupted. In Fig. Ethenurmal'relation is shown at the instant'ofstopping of arm 43 at the end of a revolution. The normal stop intervalis the'timerequired for the ring to move from it's Fig; 3 position toits Fig. 2 position.

If now the brush ring is too fast, the parts will reach thepositionshown in Fig. 2 in advance of the, receipt of-the startpulse'from the "distant station and the brush ring will be stopped untilthe start impulse releases the arm 'If the brush ring: is runningslightly behind/the parts Will-196111 the'position shown in Fig. 3 atthe instant' of stoppage of the arm 43 because the arm 43 overtakes thelimit at at some time'during the rotation and advances'the ring tothe'Fig/3 position. The rin M, if' too slow, will not advancesufiiciently farduring the stoppage period of the arm 43 to reach theFig. ,2 position by the time .arm 43 is released, but arm 453willovertalze the ring at sometime during the revolution and for theremainder of the revolution the ring will travel withthearm and at thespeed of the arm. 'Ihesrnall error with which the brushes'start out on arevolution will in this manner not be cumulative, but will again be thesame '-at thecom- There pletion of the revolution. It will be observedthat this is the opposite of the usual start-stop operation in which thebrushes are started at the correct time, but, if slow, lag farther andfarther behind during a rotation.

Referring to Figs. 4, 5 and 6, the motor I6 is mounted by suitablebrackets on the bed plate 5i! which forms part of a housing for thedistributor mechanism. the rest of the housing being indicated at 5!.Shaft H has keyed to it a pinion 52 which is formed integral with or hassecured to it a sleeve 58 extending downwardly in Fig. 5 and terminatingat its lower end in a flange 59. Mounted for rotation on this sleeve 56is a larger sleeve 51 keyed to a pinion. 55 for rotation therewith.Idler gears 53, E i communicate motion .from gear 52 to gear 55 with aslight speed increase (e. g. 2 per cent). Arm 43 is enlarged into a discsurrounding the sleeve 56 to provide relatively larg surfaces formounting between discs 58 of cork or other suitable friction material.The opposite end of the arm 43 extends toward the right in these figuresand cooperates with latch 32 and release magnet 33 in the manner alreadydescribed.

The brush carrier 44, indicated in diagram in Figs. 2 and 3 as a ringfor convenience of description, is in the actual construction shown anarm similar in general to arm 43 in that it is enlarged into a disc atone end for mounting between friction discs 6i which are in turn heldbetween flange 59 and washer 60. Arm 44 has brushes 5?. supported on itsunder side.

Arm 43 has a depending member 41 (see Fig. 6) bifurcated at its lowerend to provide two prongs 45 and 46 between which the end of the brushcarrier 44 extends. These are the limits 45 and 46 referred to in thedescription of Figs. 2 and 3. Assuming movement toward the right in Fig.6, arm 44 will under normal conditions just be coming into contact withprong 45 at the instant of reaching the stop 32 and will just be cominginto contact with prong 45 at, the instant of release of arm 43. If thebrushes are behind, prong 46 will advance the arm 44 and if the brushesare ahead, prong 45 will stop the arm 44, as has been described above inconnection with the diagrammatic Figs. 2 and 3. The friction discs 58provide sufliciently greater friction than discs 6| so that arm 43controls the motion of arm 44 in the manner described.

The invention is not to be construed as limited to the precise detailsor magnitudes that have been given herein but the scope of the inventionis defined in the claims. which follow.

What is claimed is:

1. In a rotary distributor, a brush arm rotatable with respect todistributor segments, a stop therefor, timing means defining thestarting time for each rotation of said brush arm, means to interposesaid stop in the path of said brush arm a given interval in advance ofthe normal starting time representing a small fraction of a rotationalperiod, and means controlled by said timing means to remove said stop atthe end of said small interval whereby said brush arm is stopped only ifit is in abnormally advanced phase at the instant of interposing saidstop.

2. In a rotary distributor, a brush arm rotatable with respect todistributor segments, a stop arm also rotatable, engageable meansbetween said arms for permitting said stop arm when stopped to stop saidbrush arm, timing means for defining the starting time for said stop armin ill each rotation, means for rotating said stop arm in advanced phasewith respect to said brush arm, means governed by said timing means tostop said stop arm in each rotation to permit said brush arm to approachsaid stop arm when the latter is stationary, said engageable meansstopping said brush arm only when the latter is in abnormally advancedphase with respect to said stop arm at the instant of stoppage of thelatter.

3. In a rotary distributor, a brush arm rotatable over distributorsegments, a stop arm rotatable ahead of said brush arm and at a slightlygreater rate, stop means for said stop arm, timing means to remove saidstop means to permit said stop arm to begin a new rotation, andengageable means between said stop arm and brush arm for stopping thelatter only when said brush arm overtakes said stop arm before thelatter is released.

4. In a rotary distributor, a brush arm rotatable over distributorsegments, a corrector arm rotatable with said brush arm and linkedthereto by means permitting a limited small relative movement betweensaid arms, means for driving said corrector arm at a slightly fasterrate than said brush arm, stop means for said corrector arm and timingmeans for removing said stop means periodically to permit rotation ofsaid arms.

5. A combination according to claim 4 including means for driving saidcorrector arm at such a rate in excess of the rate of motion of saidbrush arm that the corrector arm gains a distance equal to the extent ofsaid limited relative movement during the normal time between theremoval of said stop means and the next stoppage of said corrector arm.

6. In a rotary distributor, a brush arm rotatable with respect todistributor segments, and means for keeping said brush arm withincertain limits of error in phase comprising a corrector arm rotatablewith said brush arm and link means engaging said arms with a certainamount of leeway such that said corrector arm advances the brush armwhen the latter is behind normal position and retards said brush armwhen the latter is ahead of normal position.

'7. In a distributor mechanism, a segmented ring, a brush carrierrotatable relative thereto, a pair of stops on said brush carrier spacedapart by a small angular distance. a rotatable arm mounted to rotatewith said brush carrier and to have its movement with respect to saidbrush carrier limited by said two stops, means to drive said armslightly faster than said brush carrier, and means to stop said arm ineach rotation for an interval equal to the normal time of travel of saidbrush carrier through said angular distance.

8. In a start-stop distributor, a brush arm, a segmented ring. means torotate the brush arm relative to said ring, a stop for said brush arm,constructed to stop the rotation of said arm in each revolution in whichsaid brush arm is in advance of normal position, and means to removesaid stop to permit said brush arm to continue its rotation withoutinterruption in each revolution in which the brush arm arrives at saidstop in normal phase.

9. In a speech privacy system in which the speech waves are firstrecorded and then are reproduced for transmission in abnormal order,distributor means for breaking the reproduced speech into fragments forearrangement into and a brush arm rotatable thereover, a rotatable stoparm separate from the brush arm but mechanically linked thereto withprovision for for said stop arm, whereby said. stop arm may be stoppedin advanced phase with respect to 7 said brush arm, and timing means forreleasing said stop arm before the brusharm reaches the limitrof saidrelative motion in each revolution in which the brush'arm is not aheadof normal limited relative motion between said arms, a stop 5 phasepositio WILDEN A. MUNSON.

